Moved checkpoint compatibility check from slave to master.

Review: https://reviews.apache.org/r/10599

git-svn-id: https://svn.apache.org/repos/asf/incubator/mesos/trunk@1469659 13f79535-47bb-0310-9956-ffa450edef68
Fixed slave to properly schedule executor directories
for garbage collection.

Review: https://reviews.apache.org/r/10604

git-svn-id: https://svn.apache.org/repos/asf/incubator/mesos/trunk@1469660 13f79535-47bb-0310-9956-ffa450edef68